VigenereCipher

History and usage

The Vigenere cipher was named after Blaise de Vigenère. This substitutiom cipher was invented by Giovan Battista Bellaso in 1553, however, the scheme was later ameliorated by Blaise de Vigenère in the 19th century, and therefore acquired its present name. The Vigenere cipher is similar to the Caesar cipher, but is harder to break (it resisted all attempts for around three centuries).

Detailed Explanations : How it works?

1. Firstly, we'll "draw" the Vigenere Table:

2. After, we'll repeat the key:

If our message has a length of 12 for example, and our key is CRYPTOOLS, then we just repeat it until the new key length is superior to the message length:

CRYPTOOLSCRYPTOOLS

And we take the first x characters of this string, where x is our message length:

CRYPTOOLSCRY

3. We encrypt the message using the Vigenere Table:

CRYPTOGRAPHY
     |
     v
CRYPTOOLSCRY
------------
EIWEMCUCSRYW

4. We output the word

return "EIWEMCUCSRYW"

Weaknesses

• Repeating key
• Cryptanalysis can determine the key length

Implementations

Language	Encrypt	Decrypt
C	c/vigenere.c	c/vigenere.c
Python	py/encrypt.py	py/decrypt.py
JavaScript	js/encrypt.js	js/decrypt.js